Repellents have been used for as long as history has been recorded, to prevent insects, arthropods, etc., from harming or annoying subject hosts such as humans, pets and other domesticated animals, and so forth. In addition, repellents have been used to prevent harm from pests such as insects and arthropods on inanimate materials, such as clothing, furniture, foodstuffs, etc. Examples of such materials are well known, including moth balls, and citronella candles. In the 20th century, very powerful, and very toxic chemicals have been developed which either repel or kill the aforementioned pests. Examples of these include "DDT" and "DEET". (Only acronyms are given, because these compounds are extremely well known to the artisan).
The noted toxicity of the aforementioned materials has been shown to not be restricted to the pests against which they are directed. Rachel Carson, in Silent Spring, documented the effect of DDT on the environment. Recently, DEET has been implicated as a toxin and potential carcinogen. Thus, there is an interest in safe, non-toxic chemicals which are also useful as pest repellents.
Safety to the user is not the only concern with respect to these repellents. As Silent Spring and other works have shown, repellents and other toxic chemicals persist in the environment for surprisingly long periods of time. Many repellents are used outdoors, generally in pristine areas which are not exposed to toxins. These persist, generally with harmful and damaging consequences. Further, those repellents which are toxic impact the natural ecosystems to which they are released, affecting complex, evolved systems of the native fauna. As an example of this, generally dragonflies are not considered an insect pest. They breed however, in wetlands which also habituate other insects, such as mosquitoes, which are considered pests. Application of a toxic repellent to ward off mosquitoes can also harm dragonflies, especially in the larvae, or nymph phase, where food is ingested in soluble form via gills. The resulting damage to the dragonfly population results in an increase in the population of their natural prey--including mosquitoes--which can lead to increases in the spread of diseases borne by the mosquitoes.
The foregoing example is just one of a number which could be cited to show the effect of pesticides and repellents on natural systems. Given the complex interrelationships that define nature, there is much that is unknown, and much that can be disturbed, sometimes permanently.
It is thus perhaps not surprising that there is interest in repellents which are not synthetics, and which may not be toxic.
An early example of a specific repellent, i.e., one directed against a particular type of insect, may be seen in U.S. Pat. No. 173,945, to Hall et al. This patent describes a moth repellent suitable for use on articles such as furs, woolen goods and pictures. The composition contains alcohol, turpentine, tar, camphor, mirbane essence (nitrobenzene), camphor spirits, citronella essence, bitter almond essence, and cedar extract. This liquid is brushed, or sprinkled on the area to be protected.
It will be understood from the disclosure that this composition is clearly unsuited for topical application to skin or other body areas of humans or domesticated animals, as many of the items are themselves toxic or noxious.
U.S. Pat. No. 351,897 is to the same effect in that it teaches a repellent composition suitable for application to paper. The composition contains tar, petroleum, oils of cedar, pennyroyal, sassafras and citronella, as well as creosole, carbolic acid, and sulphur. This composition is incorporated in, rather than applied to the paper, as it is added during the pulping process, or impregnated therein
Bishopp et al., J. Econ. Entomol 18: 776 (1925) discusses the results of "test jar" experiments In these, a meat sample is coated with the material to be tested and is placed in a jar After a given period of time, the meat is studied for insect reaction. The reference states that some of the "essential oils", e.g., Oils culled from the essences of various plants and plant parts, show promise. Citronella, fennel, camphor (crude), clove bud oil and clove powder are mentioned.
In an extensive study, Parman et al., Technical Bulletin No. 80 (September 1928, U.S. Dept. of Agriculture) studied various substances to determine if they were effective against blow flies. The goal was to find prospective wound treating agents. In Table 9 of this reference, various essential oils were tested. Of 26 of these, three of the oils of the invention, i.e., citronella oil, pennyroyal oil, and camphor oil, were ranked 15th, 19th and 20th in terms of efficacy. Camphor oil, in fact, attracted insects of one species.
U.S. Pat. No. 2,041,264 describes various emulsions, one of which may contain citronella oil. Such emulsions are said to have insect repellent properties, although no empirical evidence supports this, at least in the cited patent.
By 1957, one sees a turning away from natural insecticides as Hall et al., Insect Repellents and Attractants 5(9): 663 (Sept. 1957) espouse the use of DDT and state that oil of citronella, pennyroyal, cedar, and camphor are "obsolete" because while they have a certain efficacy and limited repellency toward mosquitoes, this is "short lived". Indeed, this turning away from the essential oils is continued in U.S. Pat. No. 2,302,159, to Wasum, who says that citronella has a "strong unpleasant odor" and that some of the essential oils are annoying and possibly harmful against tender or sunburned skin.
In U.S. Pat. No. 4,193,986, a flea treatment composition is described. The vast majority of the composition (93-98%) is inert. The remaining, active fraction contains pennyroyal (10-40 parts), eucalyptus oil (5-20 parts), cedar oil (3-10 parts) citronella oil (5-10 parts), and oil of rue (1-2 parts). The preferred composition is 17-32 parts pennyroyal, 8-16 parts eucalyptus, 5-8 parts cedar, 5-8 parts citronella, and 1.25-1.75 parts rue. This material is designed for use on animals previously infected with fleas.
The ubiquitous citronella is used again in U.S. Pat. No. 4,320,112, where it is combined with naphthalene to form a pest repellent for garbage bags and the like.
U.S. Pat. No. 4,671,960 teaches a flea repellent. A collar device is taught and contains both plant solids (pennyroyal, eucalyptus, camomile), and small amounts of the oils of pennyroyal, eucalyptus and citronella.
This survey of the art shows that there is no teaching of the invention, which is a topical composition useful as a pest repellent, this composition comprising equal parts of the natural oils of citronella, cedar and wintergreen in a non-toxic carrier. It has been found, surprisingly in view of the art, that these compositions are effective when applied to human subjects. Further, by using an oil base, it has been found that a surprisingly large amount of effect ingredient, i.e., anywhere from 15-40 parts of the total composition, may be the active mixture. In tests in the field, the compositions of the invention not only performed effectively but did not aggravate the skin of subjects who were exposed to extremes of heat and humidity.
The invention is described in more detail in the description which follows.